In order to optimize electrical performance in brushless DC motors in terms of improved efficiency, power factor, and reduced current, it is important to be able to determine the angular position of the rotor. It has been possible to determine the position accurately, but not absolutely with some techniques such as with a null detector which is essentially an incremental sensor that can be used for counting and determining velocity. While a null detector is very accurate, and is not adversely affected by the effects of temperature and the like, it cannot determine the angular position of the rotor in an absolute sense.
On the other hand, it has been possible to determine the angular position of a rotor absolutely, but not accurately with some other techniques, such as with an absolute sensor that measures the distance between the sensor and the rotating wheel where the distance is continuously variable. While an absolute sensor can be utilized where temperature variations are negligible, and is well-suited for use as a counter for determining the number of revolutions, it is not well-suited where accuracy is important in an atmosphere of variable temperature and the like.
In the past, it has been proposed to utilize a stationary magnetic sensor to determine the angular position of a rotor in an accurate but not absolute sense. This is proposed, for instance, in Rothley et al U.S. Pat. No. 4,506,217 which also senses speed, and an Sato et al U.S. Pat. No. 4,369,405 which discloses an AC power generated apparatus utilizing rotating magnet poles. In addition, Glauert et al U.S. Pat. No. 4,166,977 also discloses a rotary speed and angular position determining system.
Still other speed and position detecting apparatus are disclosed in U.S. Pat. Nos. 4,370,614; 4,490,674; 4,481,469; 4,506,339; 4,359,685; and 3,728,565. Nevertheless, it has remained to provide a position detecting apparatus using multiple magnetic sensors to determine angular position of a rotor accurately and absolutely whether stationary or rotating.
The present invention is directed to overcoming the above-stated problems and accomplishing the stated objects.